I've been thinking about it, and I've decided this: the royal engagement outfit has to be one of the hardest outfits in royal life to get just right.
First of all, it's not an everyday business meeting. (Well, I suppose once upon a time it was a business meeting, but I should hope we've moved past that by now.)
Second, it may not be an every day event, but it's still not an evening occasion - Sophie's engagement suit I recall being criticized as too "evening" just because she went for a little beading. And there's something off about Charlene in a long dress next to Albert in a regular old suit.
Thirdly, one must be careful not to date oneself.
Yes, timeless is the way to go. Princess Elizabeth looks well-dressed even 60 years later.
Now, let us revisit the case of Miss Catherine Middleton:
Tell me: who tops your all-time best dressed royal fiancée list, and where does Kate rank on your list?